A Nobel Prize-winning scientist has reportedly said all Britons should be tested for variant CJD.

Professor Stan Prusiner, who discovered the cause of BSE, said the government should also be testing live animals for the disease.

Presently, the only surefire test for the "prion proteins" that cause the illness is carried out post mortem.

However, blood and even urine tests for the prions are under development - although they may not be reliable for some time.

Speaking on a visit to Britain from his native US, he claimed thousands of infected cows and sheep were still entering the human food chain.

So far, CJD has killed 117 people in Britain since 1995 and another 11 are dying from the disease.

No cure

According to the Sunday Times newspaper, Professor Prusiner said: "A million cattle infected with BSE entered the British food chain [in the past] so almost everyone in this country will have been exposed to the infectious prion proteins that cause variant CJD.

"Every Briton should be tested so that if they are developing the disease it can be spotted before symptoms appear."

Although there is no cure for CJD, detection may help prevent further infection via blood donations or surgical instruments.

A Department of Health spokesman, responding to Professor Prusiner's comments, said: "We have set up a number of expert committees to review various developments in both the assessment and treatment of CJD.

"We would ask them to assess the validity of any new finding including tests, before we decided how we might use them."

The professor said cows and sheep should be tested because they were being slaughtered before they showed the clinical symptoms of BSE.

He also indicated muscle and flesh of cattle and sheep could harbour prions - raising the prospect that today's meat could still be infected.

Prions can lie dormant in the body for up to 40 years, so estimates of the scale of the epidemic vary.

But there is some opposition to human testing because some fear the knowledge can only bring misery and maybe spark huge compensation claims.

Professor Prusiner, from the University of California, was awarded the Nobel Prize for medicine in 1997.

Last week, research in London suggested the number of CJD cases could be higher than previously thought because BSE-infected meat may cause "sporadic" as well as variant CJD.